1. Field of the Invention
This invention relates to electric switches, and particularly to high power electric switches having an enclosed envelope and suitable for making, breaking and carrying high levels of direct current in the order of 25,000 amperes.
2. Description of the Prior Art
It is believed the prior art relating to the subject matter of this invention may be found in Class 200, sub-classes 82R; 16B; 153S and 255. Additionally, art pertaining to this invention is believed to reside in Class 335, sub-classes 182, 183 and 184. The inventor herein is the inventor named in U.S. Pat. No. 3,941,957 and is aware of and hereby notes and includes herein by reference the reference patents cited in that patent.
The prior art is repleat with switches of various designs. For instance, the inventor herein joined in the conception and design of the devices taught in U.S. Pat. No. 3,368,049 entitled High Current Radio Frequency Switch, and U.S. Pat. No. 3,394,324 entitled Coaxial Switch. Additionally, the inventor herein is the inventor named in U.S. Pat. No. 3,941,957. The switches forming the subject matters of these patents, with the exception of U.S. Pat. No. 3,941,957, and many conventional switches have incorporated a vacuum envelope within which the contacts make and break a circuit through the switch. The inventor herein has pioneered vacuum type radio frequency switches such as exemplified by the above noted patents and U.S. Pat. No. 3,261,953. One disadvantage inherent in a vacuum switch is that the cost of processing the vacuum switch tends to be prohibitive. Accordingly, it is one of the objects of the present invention to provide an electrical device in the nature of a switch which is capable of making, breaking and carrying high levels of direct electrical current without the necessity of providing a vacuum envelope.
Additionally, because the atmosphere within the sealed envelope constitutes a high vacuum, it is especially difficult to achieve movement of parts relative to one another within the vacuum envelope without a certain amount of galling. The reason for such galling is that the surfaces of the metallic parts within a vacuum switch are so clean and free from oxidation that two metal parts that come together tend to stick and weld together and resist relative movement. On the other hand, prior to my innovations, particularly the innovations described in U.S. Pat. No. 3,941,957, it was not practicable within the state of the art to produce a radio frequency switch that had the voltage standoff characteristics required for wide applicability without using a vacuum envelope. Additionally, vacuum switches are physically fragile and not susceptible to connection with high power busses. Accordingly, a still further object is the provision of a non-vacuum switch structure that is rugged and well suited to connection to heavy, high current busses.
With respect to high levels of direct and alternating current, it has not heretofore been practical to make, break or carry such direct and alternating currents because of the tendency of the switch contact to arc in both the "make" and "break" modes, because of the excessive heat generated when the switch is in a "carry" configuration, and because of the inherent danger surrounding the installation and operation of such switches. Accordingly, another object of the present invention is to provide a switch structure capable of effectively handling high levels of direct and alternating current without the danger of arcing, or the disadvantage of heating, or the inability to carry high levels of current in the order of 25,000 amperes.
Another of the disadvantages of conventional vacuum switches is that these switches require the use of an external actuator to effect transfer or movement of the contact within the envelope. The use of external actuators has run the gamut from hydraulic to air, to solenoids, and to mechanical linkages adapted to effect transfer of the movable contact within the envelope. All such external actuators have required the utilization of a deformable vacuum type wall in the nature of a flexible bellow or diaphram interposed between the movable contact and the actuating mechanism. Where a solenoid has been used, it has been necessary to provide a vacuum tight seal between the coil structure of the solenoid and the armature thereof on which, or in association with which, is mounted the movable contact within the vacuum envelope portion of the switch. The use of such vacuum tight sealing methods and materials has required the utilization of special skills and fabrication techniques which contribute to the prohibitive cost of such devices. Accordingly, it is another object of this invention to provide a switch structure in which the contact element makes and breaks a circuit within a fluid medium rather than in a vacuum.
So far as is known, a switch structure has not been patented or successfully used in which two movable electrically conductive members are provided within a sealed but not vacuum envelope with one of those movable members functioning to make or break a circuit between associated terminal members and therefore appropriately constituting a "contact", and the other movable member constituting a conductive bridge or shunt in relation to the movable contact member to provide two paths for current flow through the switch. Both of the movable members constitute pistons mounted for displacement between switch "open" and switch "closed" positions by the imposition of fluid pressure applied directly to the pistons within the envelope. Accordingly, it is a still further object to this invention to provide a switch structure particularly suitable for high levels of direct and alternating current in which movement of the make or break contact and current conductive bridging elements is controlled by direct application of fluid pressure thereto.
In the operation of high level direct and alternating current switchgear, one of the forces that tends to "open" the switch contacts of such switchgear, thus increasing the contact resistance, and thereby lowering the current carrying capacity thereof, is the magnetic field that surrounds the switch contacts and tending to drive them apart. Accordingly, another object of the present invention is the provision of a switch structure that effectively cancels the magnetic field effect that tends to drive the contacts apart when the switch is in a current "carry" mode.
The susceptability of switches to arcing between relatively movable members is well known. This is particularly true in a switch which is utilized in high current applications. One of the factors that initiates such arching is contact "bounce" upon closing of the switch at high closing velocities. Accordingly, it is another object of the present invention to provide a high direct current switch incorporating a contact assembly and method of actuation thereof which incorporates a built in resilience and resistance to contact bounce, thus reducing or eliminating the tendency of the contact to generate an arc.
Among the factors that determine the circuit breaking characteristics of a switch is the efficiency with which heat generated in the contact elements is dissipated. It is well known that permitting the contact element to operate at elevated temperatures increases the electrical resistance and thus lowers the current carrying capacity of the switch. This problem has been partially solved in the art by fabricating the movable contact member of material possessing a large mass, the thought being that such large mass functions as a heat sink. This solution however introduces a new problem, namely, an increase in the inertial force when the switch contact of large mass moves at high velocity from one position to another. Such high inertial force contributes to contact bounce and to arcing between the contact surfaces. Accordingly, it is yet another object of the present invention to provide a contact assembly for a high direct and alternating current switch in which the contact assembly includes a piston movable between requisite positions by the direct imposition of fluid pressure thereon, which also serves to absorb and convey away a large proportion of the heat from the switch contact, and which works in conjunction with a piston-like highly conductive bridge member that provides a multiplicity of short current-carrying paths between the terminals to thereby increase the current-carrying capacity of the switch.
In prior art switches touted as "no bounce" switches, one of the contact members is usually stationary while the movable contact is mounted on an appropriate support which also functions as the means for moving the contact. Such means frequently constitutes a slide bearing and a spring. One of the reasons why such prior art switches do not successfully achieve a "no bounce" condition is that there is no appreciable resilience in the stationary contact, so that when the movable contact impinges against the stationary contact at high velocity, there is no means provided to prevent the contacts from bouncing apart. Accordingly, another object of the present invention is the provision of means associated with both of the "make" and "break" contact members in a high level direct and alternating current switch to completely eliminate bounce between the contacts.
One of the limiting factors in connection with high radio frequency switches is the "skin effect" as frequencies increase, which may be described as limiting the current carrying capacity of the conductor to the peripheral surface thereof as distinguished from its cross-sectional area. The opposite is generally true with direct and low alternating current conductors, the effectiveness of the conductor and its current carrying capacity being determined by its cross-sectional area. This factor has been one of the limitations in high level direct and alternating current switches for the reason that there has been a practical limit to the diameters of current carrying members that could be used in conventional direct and alternating current switches. Accordingly, another object of the present invention is the provision of means to increase the effective cross-sectional area of the conductors in a direct and low alternating current switch so as to increase to a surprising level the current carrying capacity of the switch. For instance, because of the technological break-through presented herein current levels of 25,000 amperes and above now appear to be routinely possible because of the novel structure described herein.
It is sometimes difficult in an art such as the one here involved to explain why a specific structure such as herein described operates in the way that it does, while a somewhat similar yet conventional structure, with seemingly small differences in mechanical configuration and mode of operation will not operate by the same mode nor to the expected level. This phenomenon has been encountered in the development of the switch forming the subject matter of this invention. It can be affirmed that, surprisingly, the switch structure illustrated and described herein has surpassed a current carrying capacity of 25,000 amps. continuous and has successfully closed in on a circuit carrying such amperage and interrupted such high levels of amperage without generation of destructive arcs.
Conventional direct and low alternating current switches have attempted to eliminate the arcing problem by designing contact structures that will automatically extinguish an arc after it has formed. One of the objects of the present invention is the provision of a switch structure for direct and alternating current loads that prevents such as arc from forming so that the problem of extinguishment of the arc is eliminated.
Still another object of the invention is the provision of a high level direct and alternating current switch which possesses a total resistance when closed of only about 1.6 micro-ohms at a temperature of approximately 160.degree. F..
A still further object of the present invention is the provision of a high level direct and alternating current switch incorporating a sealed envelope enclosing therewithin movable members forming electrical conductors that move at a predetermined velocity under the impetus of a predetermined fluid pressure differential to effect closing or opening of the switch without the generation of a destructive arc.
A still further object of the present invention is the provision of a method of operating a switch structure of the type described to achieve a high current carrying capacity without generation of destructive arcs.
Still another object of the invention is the provision of a high current carrying contact strip for use in high energy switch structures.
Another object is the provision of means in a high level switch structure for effecting rotation of large diameter current carrying members to eliminate galling of the contact surfaces thereof.
Yet another object of the invention is the provision of a switch structure in which resiliently biased contact bars are periodically relieved of bias to increase their life expectancy and efficiency.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope of the appended claims.